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A090907 Ratio of products of successive rows of the irregular triangle defined in A090905. 4
2, 6, 140, 1287, 2139552000, 2949442889323392, 322686644032484531917367528014184448000000 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Conjecture: For n > 4 the last term of the n-th group is 2p where p is the largest prime in the (n-1)th group. And these are the Bertrand primes.

LINKS

Table of n, a(n) for n=1..7.

EXAMPLE

a(1)=(2!/1!)*(0!/1!)

a(2)=(4!/2!)*(1!/2!)

a(3)=(8!/4!)*(2!/4!)

a(4)=(14!/8!)*(4!/8!)

a(5)=(26!/14!)*(8!/14!)

a(6)=(46!/26!)*(14!/26!)

For n>=6 we have a(n)= ((2*A006992(n))!/(2*A006992(n-1))!)*((2*A006992(n-2))!/(2*A006992(n-1))!), verified for 4<n<21

CROSSREFS

Cf. A090904, A090905, A090906.

Sequence in context: A156515 A254223 A206849 * A159478 A047937 A027731

Adjacent sequences:  A090904 A090905 A090906 * A090908 A090909 A090910

KEYWORD

nonn

AUTHOR

Amarnath Murthy, Dec 13 2003

EXTENSIONS

Edited by Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 05 2004

STATUS

approved

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Last modified November 21 14:18 EST 2019. Contains 329371 sequences. (Running on oeis4.)